Latent image intensification with sulfur dioxide



invention Patented Mar. 9, 948

LATENT. IMAGE INTENSIFICATION WITH SULFUR DIOXIDE Walter J. Weyertsand Charles w. Wiederhold,

Rochester; N; Yi, assignors'to=Eastman-'Kodak- Company, Rochester,

New J ersey i 1;, a. corporation of P V No Drawing. 'Applicat ion July 26; 1945; Serial 5 Glaims. (Cl; 95-43) This invention relates to photography and particularly to a method of intensifying-- a photographic latent image.

In SimmonsU; S. Patent 2,368,267, granted January 30; 1945; a'method for intensifying latent I images is described according to whichan exposed" silver halide emulsion: layer is treated before development with sulfur dioxide gas; and then" removed from the source of sulfur dioxide gas and stored for a period of timeprior todjeve'lopment. This method produces" satisfactory intensification of the latent image and an effective increasein speed. of.-the sensit-ive material. However, it generally required-long. treatment times. If the sensitive material was kept in the atmosphere of sulfur dioxide fora shorttime, it has-to bestored'for: about two days inair tosecure thedesired increase inspeed. On the other'hand, if: thel'materi'al were treated with sulfur dioxide fora long period, the time of air storage could be shortened but: the total time of treatment remained considerable.

Itis therefore an object of the presentinvention to provide a method for latent image intensification of photographic. silver halide materials which does not require. a long treatment time between exposure and development of the material. A further object is to provide a method for increasing the emulsion sensitivity or speed oi photographic materials by a simple and rapid post exposure treatment so that thesensitive male terials may be used under light conditions which previously'had-been' consideredunsatisfaotory. A stillfurther object is to provide a rapid'method for treating, underexposed: films such as motion picture films to permit their salvage and utilization to formasatisfactory image. Other objects will: appear from the following. descriptionoii our These objectsareaccomplished by bathing an exposed silver halide, emulsion layer, prior. to development in. an aqueous solution of sulfurous acid or a material which gives sulfurous acid in solution such as sodium bisulfite or potassium meta-bisulfite.

According to our invention, films or plates containing photographic'latent images are bathed for approximately one minute in an aqueous solution of sulfurous acid or a material which furrushes-sulfurous acid-in aqueous solution, such as sodium bisulfite, NaHSOs-or potassium meta-bisulfite K2S2O5. Alkali metal salts of other-oxygen acids of sulfur which produce sulfurous acid in solution may be used. The sulfurous acid bath should not contain photographic developing In Great Britain November 8,

. 2 agents-or materials whichact' as anti-oxidants such as hydroquinone or iso-a-scorbic acid; Such materials completely arrest any latent image intensification and should therefore be excluded from the sulfurous acid bath. The pH of the bathshould be maintained below about pH 6. The intensification of the latent image increases with increase in pH of the sulfurous acidbath but with the pH. values above about pH' 6 fog increases rapidly with rise in pH; I V I After treatment. in the sulfurous acid solution, the films or. plates areremoved from the solution and the excess liquid removed from their surfaces by aid of an air squeegee or by wiping with a suitable material. They are then placed where air. is free; to circulate around them,-f ,or 10; to,

minutes-:01 longer after. which they; aredeveloped A high speed intheusualmanner.

. The storage of the. material. in. air after treat.- mentin thesulfurous acidrsolutionis an essential featureofour. process. We have found that 10 orminutes is a suificient length oftimeto' hold the treated: material. in air, although. a longer period of time a does noharm. The temperature and humidity ofthe air shouldbe maintained at a point where no undue softening of the. swollen, unhardenedoemulsion takes place. Althoughifree circulation of air around photographic material during the-holdingi period is desirable to obtain the maximum increase in sensitivity, a rapid circulation of air gives only little improvement over that obtained by merely hanging up. a. treated film in a darkroom for therequired time. However, a film which has been treatedi andthen 35 placed in a small closed container during the'holding-periodgives less increase inispeed;

Our invention: will be further illustrated by reference to the following. examples. In. comparing the effect of treatment in sulfurous acid solutions of exposed gelatino silver halide emulsions, with a; control,,iti was. found desirable to bathethecontrol in distilled water-for the same length. of: time the material being tested was bathed in the-sulfurousacid solution; Ehereason for this is that merely bathing a film: in water before :development gives, a slight increase 'inspeed over theoriginalwhen both are developed under the :samesconditions. For 'thisreason the controls were-bathed distilled water andthenwere held under conditions similar tothe treatedfilm before de e men v. wm l l 3.: 3: negative gelatino silver halide emulsion such as Kodak Plus X was exposed on a standard sensitometer, for example, Eastman 3 Type 2B sensitometer, and portions or the film were then bathed in distilled water, in a 1% aqueous solution of sodium bisulfite and in a 1% solution of potassium meta-bisulfite for 1 minute.

having a pH below about 6 and being free of photographic developing agent and other antioxidant, removing the layer from the solution and storing it in air for an appreciable period of time and then developing an image in said layer.

2. The method of increasing the sensitivity of a gelatino-silver halide emulsion layer which comprises exposing said layer to an actinic light image, immersing the undeveloped layer in an aqueous solution of sodium bisulfite having a pH below about 6 and free of photographic developing agent and other anti-oxidants, removing the layer from the solution and storing it in air for an appreciable period of time and then developing an image in said layer.

3. The method of increasing the sensitivity of a gelatino-silver halide emulsion layer which comprises exposing said layer to an actinic light image, immersing the undeveloped layer in an aqueous solution of potassium meta-bisulfite having a pH below about 6 and free of photographic developing agent and other anti-oxidants, removing the layer from the solution and storing it in air for an appreciable period of time and then developing an image in said layer.

4. The method of increasing the sensitivity of a gelatino-silver halide emulsion layer which comprises exposing said layer to an actinic light image, immersing the undeveloped layer in a 1% solution of sodium bisulfite having a pH below about 6 and free of photographic developing agent and other anti-oxidants, removing the layer from solution and storing it in air for ap- Eacirof these films was then removed from the solu ion and was held in air in the darkroom for 10 nutes. It was then developed in a solution of t e following composition:

I Grams Monomethyl-p-aminophenol sulphate 2.0 Hydroquinone 5.0 Sodium sulfi 100.0 Boric acid 8.0 Borax 8.0 Potassium bromide .25 Water to l-liter The films were then fixed in the usual way and the values for speed, gamma and fog were determined. The emulsion speeds were read as 30/]?! at a density of 0.3 above base color plus i'og where E is exposure in meter candle seconds. The following results were obtained.

Density 30/E Speed Gamma oi 1232c Control:

Bathed in dist. Hi0 for 1 minute, held 10 minutes in sin-.- 2, 550 0. 94 0.27 Bathed in 1% NaHSOz for 1 minute, held in air for 10 minutes 3,800 0.84 0. 27 Bathed in 1% K SzOs for 1 111111- ute, held 10 minutes in air.-.. 7,050 0.73 0.26

Example 2 g A film such as that described in Example. 1 was exposed in the same-way as in Example 1 and portions of the film were then bathed for one minute in distilled water and in 1%, 2%, 5% and 10% aqueous solution of potassium metabisulfite. The film were then removed from the solutions and stored in air for 10 minutes after which they were developed in the same manner as in Example 1. The values'for speed, gamma 7 and fog were then determined with the following results.

Density 801E Speed Gamma 053320 Control:

Bathed in dist. H10 for 1 minute, held in air for 10 minutes. 3,200 0.95 0.28 Bathed in 1% K1810; for l minute, hold in air for 10 minutes. 4, 550 0.83 0.30 Bathed in 2% K1810; for 1 minute, held in air for 10 minutes. 5,850 0.73 0.31

Bathed in 5% K1510; for l minute, held in air for 10 minutes- 6, 0. 76 0. 32

Bathed in 10% K1820; for 1 minute, held in air for 10 minutes 5,000 0.82 0.30

It will be understood that the examples and modifications included herein are illustrative only and that our invention is to be taken as limited only by the scope of the appended claims.

What we claim is:

' acid in solution, said first-mentioned solution proximately 10-20 minutes and then developing an image in said layer.

5. The method of increasing the sensitivity of a gelatino-silver halide emulsion layer which comprises exposing said layer to an actinic light image, immersing the undeveloped layer in a 1% solution of potassium meta-bisulfite having a pH below about 6 and free of photographic developing agent and other anti-oxidants, removing the layer from solution and storing it in air for approximately 10-20 minutes and then developing an image in said layer.

WALTER J. WEYERTS.

CHARLES W. WIEDERHOLD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Image, Journ. Franklin Inst. 203 February 1927, pages 261 to 287 (pages 279 to 281 cited). (Copy in S. L.)

Bullock, Chemical Reactions of the Photographic Latent Image, Eastman Kodak Co., 1927 (pages and 146 of interest). (Copy in Division 7.) 

